Idle Speed Adjustment on a Harley-Davidson Sportster

Before you do this you may need to remove the plug covering the idle mixture screw. You can find the directions on how to do that here.

Here's my version of the idle mixture adjustment procedure. It may be slightly different than others, but I believe the idea is the same.

Procedure

1. warm up the bike to operating temperature. This is very important!
2. leave the bike running and turn the idle speed screw up so the engine idles fairly fast. It is not important how many RPM at this point, this is just to prepare for the next step.
3. turn the idle mixture screw in all the way until is seats (be gentle do not tighten the screw down. It is not a fastener, it is an adjustment needle, really). If the bike stalled while doing that go back to previous step and raise the idle speed a bit more. The idea here is to have the bike idling with the mixture screw turned all the way in.
4. now slowly turn the idle speed screw in until the engine just barely runs almost stalling. You can go to the point of stalling and back off slightly from that. Now you have your idle speed set in a pretty good place. Leave it be.
5. Shut off the engine and turn the idle mixture screw out about 3 or 4 turns out. Restart the engine. It should be running just fine now. Now turn the mixture screw in slowly while listening to the engine speed. As soon as you hear the speed change (slow down) ever so slightly stop and back off a quarter turn for colder weather and half a turn for warm weather. I tend to set it at somewhere in between and forget about it.
6. If you have a tachometer, check the idle speed against it. The specification is 1,050 RPM. It is really important to idle the bike around that speed as the oil pump does not produce enough flow to protect the engine at lower speeds.
7. Test ride and enjoy!

Note: I know I am omitting the part of finding the rich stumble, but the reality is that many times there will be no rich stumble and people will go increasing their pilot jets, which is wrong. You choose your pilot jet based on other things. Once the pilot jet is chosen you adjust the idle mixture as described above and all will be well.